Origins of the genetic code: Study finds textbook version needs revision

Despite their incredible diversity, nearly all life forms, from bacteria to blue whales, share the same genetic code. How and when this code was created is the subject of much scientific debate.

Sosan Wehbi, a doctoral student in the Graduate School of Genetics Interdisciplinary Program at the University of Arizona, takes a new approach to an old problem and says the textbook version of how the universal genetic code evolved needs revision. We found strong evidence that this is the case.

Webby is the lead author of a research paper published in the journal PNAS suggesting that the order in which amino acids, the building blocks of the code, are recruited is inconsistent with what is widely considered to be the “consensus” of the evolution of the genetic code. Published in.

“The genetic code is an amazing sequence of DNA or RNA that contains a sequence of four nucleotides that is translated into a sequence of proteins using 20 different amino acids,” said the paper’s senior author, Ecology said Joanna Maskell, professor of evolutionary biology. “It’s a mind-bogglingly complex process, but our code is amazingly good. It’s near optimal in every way, and it must have evolved in stages.”

The study found that while early life forms preferred small amino acid molecules over larger, more complex amino acid molecules that were added later, amino acids that bind to metals were bound to metals much earlier than previously thought. It became clear that Finally, the research team found that today’s genetic code was likely created after other codes that have since become extinct.

The authors argue that our current understanding of how code evolved is flawed because it relies on misleading laboratory experiments rather than evidence of evolution. For example, one of the foundations of the traditional view of the evolution of the genetic code is based on the famous Ury Miller experiment of 1952, which attempted to simulate conditions on the early Earth that likely witnessed the origin of life. Masu.

Although valuable in demonstrating that inanimate objects can produce the building blocks of life, such as amino acids, through simple chemical reactions, the experiment’s significance has been questioned. For example, even though early Earth was rich in the element sulfur, no sulfur-containing amino acids were produced. As a result, sulfur amino acids are thought to have joined the code much later. However, this result is not surprising considering that sulfur was omitted from the experimental composition.

According to co-author Dante Lauretta, Regents Professor of Planetary Science and Cosmochemistry at the University’s Lunar and Planetary Institute, the sulfur-rich nature of early life is especially important for understanding the potential habitability and biosignatures of extraterrestrial environments. It is said to provide insights into astrobiology.

“In worlds where sulfur compounds are prevalent, like Mars, Enceladus, and Europe, highlighting similar biogeochemical cycles and microbial metabolism could help in the search for life,” he said. “Such insights may help us refine what we look for in biosignatures and help us detect life forms that thrive in sulfur-rich or similar chemistries beyond Earth.”

The researchers used a new method to analyze amino acid sequences across the tree of life, all the way back to the Last Universal Common Ancestor (LUCA). LUCA is a hypothetical group of organisms that lived approximately 4 billion years ago and represents the common ancestor of all living things. Life on Earth today. Unlike previous studies that used full-length protein sequences, Wehbi and her group focused on protein domains, or shorter stretches of amino acids.

“If you think of proteins as cars, domains are like wheels,” Webbi says. “It’s a part that can be used in a variety of cars, and wheels have been around much longer than cars.”

To understand when a particular amino acid may have been incorporated into the genetic code, the researchers used statistical data analysis tools to trace back from LUCA to determine the enrichment of individual amino acids in protein sequences. compared. Amino acids that appear preferentially in ancient sequences were probably incorporated early. Conversely, the LUCA sequence is depleted of amino acids that were later replenished but became available by the time the older protein sequence appeared.

The research team identified more than 400 sequence families that trace back to LUCA. More than 100 of them were even older and already diversified before LUCA appeared. Even though these amino acids were added later to the code, they were found to contain more amino acids with aromatic ring structures, such as tryptophan and tyrosine.

“This gives us hints about other genetic codes that existed before ours and have since disappeared into the abyss of geological time,” Maazel said. It seems like she used to like rings.